An automobile steering device is configured as illustrated in FIG. 8, and is such that the rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering-gear unit 2, and as the input shaft 3 rotates, a pair of tie rods 4 are pushed and pulled, which applies a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear-end section of a steering shaft 5, and the steering shaft 5 is passed in the axial direction through a cylindrical shaped steering column 6, and in this state, is rotatably supported by the steering column 6. The front-end section of the steering shaft 5 is connected to the rear-end section of an intermediate shaft 8 by way of a universal joint 7, and the front-end section of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9.
A steering wheel position adjustment device that includes a tilt mechanism for adjusting the up-down position of the steering wheel 1 according to the stature and driving posture of the driver, and/or a telescopic mechanism for adjusting the forward-backward position of the steering wheel 1 is assembled in the steering device for an automobile (refer to JP2009227181 (A)). In order to construct the tilt mechanism, a housing 10 is fastened to the front-end section of the steering column 6, and the front-end section of the upper portion of the housing 10 is supported by the vehicle body 11 by a tilt shaft 12 that is arranged in the width direction so as to be able to pivotally displace. In this specification, the width direction means the width direction of the vehicle, and coincides with the left-right direction of the vehicle. A displacement bracket 13 is provided on the bottom surface of the middle section in the axial direction of the steering column 6, and a support bracket 14 is provided in a state so as to sandwich the displacement bracket 13 on both sides in the width direction. A pair of long tilt holes 15 that extend in the up-down direction are formed in the support bracket 14, and through holes 16 are formed in portions of the displacement bracket 13 that are aligned with part of the long tilt holes 15. In the example in the FIG. 8, in order to construct the telescopic mechanism, the through holes 16 are constructed by long holes (long telescopic holes) that extend in the forward-backward direction. Moreover, the steering shaft 5 and the steering column 6 are configured so as to be able to extend and contract. A rod-shaped member 17 is provided that passes in the width direction through the long tilt holes 15 and the through holes 16. By adjusting the force by which the support bracket 14 holds the displacement bracket 13 on both sides in the width direction by operating an adjustment lever that is provided on one end section of the rod-shaped member 17, the state can be switched between a state in which the position of the steering wheel 1 can be adjusted and a state in which the position is locked.
FIG. 9 and FIG. 10 illustrate an example of a steering device that includes a steering wheel position adjustment device. The steering column 6 is configured such that the overall length can expand and contract by the front end section of an outer column 18 that is arranged on the rear side fitting with the rear section of an inner column 19 that is arranged on the front so as to be able to slide. The outer column 18 is made by die-casting a light alloy. By providing a slit 20 in the front section of the outer column 18, the inner diameter of the front section of the outer column 18 is able to elastically expand and contract. A pair of held plate sections 21 of the displacement bracket 13 are provided in portions of the outer circumferential surface of the outer column 18 located on both sides in the left-right direction of the slit 20. Through holes 16 (long telescopic holes) are formed in the pair of held plate sections 21. A pair of support-plate sections 22 of the support bracket 14 are arranged so as to hold the displacement bracket 13 from both sides in the left-right direction. Long tilt holes 15 having a partial circular arc shape that is centered around a tilt shaft 12 (refer to FIG. 8) are formed in the pair of support-plate sections 22. The rod-shaped member 17 is inserted in the width direction through the long tilt holes 15 and the through holes 16.
An adjustment lever 23 that is provided on one end section in the axial direction of the rod-shaped member 17, an anchor section 24 that is provided on the other end section in the axial direction of the rod-shaped member 17, and a cam device 25 that is provided in a portion near one end in the axial direction of the rod-shaped member 17 form a tilt locking mechanism that expands or contracts a space between the inside surfaces of the pair of support-plate sections 22 based on pivoting of the adjustment lever 23. The anchor section 24 has a shape like the head section of a bolt and is provided on the other end section in the axial direction of the rod-shaped member 17, and a pair of engaging convex sections 26 that are formed on the inside surface of the anchor section 24 engage with the long tilt hole 15 that is formed in the other support-plate section 22 (right one in FIG. 10) of the pair of support-plate sections 22 that faces the inside surface of the anchor section 24 so that displacement is only possible along the long tilt holes 15. Therefore, the rod-shaped member 17 is able to move up or down along the pair of long tilt holes 15, however, does not rotate around the center axis of the rod-shaped member 17.
As illustrated in FIG. 11, a cam device 25 in which a drive-side cam 27 and a driven-side cam 28 are combined, is assembled in the steering wheel position adjustment device. The drive-side cam 27 is formed into a circular ring plate shape as a whole and has a center hole 29 for inserting the rod-shaped member 17 through, and the driven-side cam 28 is formed into a circular ring plate shape as a whole and has a center hole 30 for inserting the rod-shaped member 17 through. A drive-side cam surface 31 and a driven-side cam surface 32, which are uneven surfaces in the circumferential direction are formed on the surfaces of drive-side cam 27 and the driven-side cam 28 that face each other. The drive-side cam surface 31 that is provided on the inside surface of the drive-side cam 27 includes a flat drive-side base surface 33 and plural drive-side convex sections 34 that protrude inward in the width direction from plural evenly spaced locations in the circumferential direction of the drive-side base surface 33. The driven-side cam surface 32 that is provided on the outside surface of the driven-side cam 28 includes a flat driven-side base surface 35, and plural driven-side convex sections 36 that protrude outward in the width direction from plural evenly spaced locations in the circumferential direction of the driven-side base surface 35. A second engaging convex section 37 is formed on the inside surface of the driven-side cam 28.
The second engaging convex section 37 of the driven-side cam 28 engages with the long tilt hole 15 that is formed in the one support-plate section 22 (one on the left side in FIG. 10) of the pair of support-plate sections 22 that faces the inside surface of the driven-side cam 28 so that only displacement along the long tilt holes 15 is possible. Therefore, the driven-side cam 28 is able to move up or down along the long tilt holes 15, however, does not rotate centered around the shaft of the driven-side cam 28. The base-end section of an adjustment lever 23 is joined and fastened to the drive-side cam 27, and the drive-side cam 27 is configured so as to rotate back-and-forth around the rod-shaped member 17 as the adjustment lever 23 is pivoted back-and-forth.
When adjusting the position of the steering wheel 1, the adjustment lever 23 is pivoted in a specified direction (typically downward), which rotates the drive-side cam 27 in the unlocking direction (right direction in FIG. 12), which is the direction of rotation when switching to the unlocked state, and as illustrated in FIG. 12A, by arranging the drive-side convex sections 34 and the driven-side convex sections 36 so as to alternate in the circumferential direction, the dimension in the axial direction of the cam device 25 is contracted and the unlocked state is set, and the space between the driven side cam 28 and the anchor section 24 is expanded. As a result, the surface pressure at the areas of contact between the inside surfaces of the pair of support-plate sections 22 and the outside surfaces of the pair of held plate sections 21 decreases or is lost, the inner diameter of the front-end section of the outer column 18 elastically expands, and the surface pressure at the area of contact between the inner-circumferential surface on the front-end section of the outer column 18 and the outer-circumferential surface of the rear-end section of the inner column 19 decreases. In this state, the up-down position and the forward-backward position of the steering wheel 1 can be adjusted within the range that the rod-shaped member 17 can move inside the long tilt holes 15 and the through holes 16.
In order to maintain the steering wheel 1 at a desired position, the adjustment lever 23 is pivoted in the opposite direction (typically upward) after the steering wheel 1 has been moved to the desired position, which rotates the drive-side cam 27 in the locking direction (left direction in FIG. 12), which is the direction of rotation when switching to the locked state. As illustrated in FIG. 12B, when the drive-side cam 27 is rotated in the locking direction, drive-side inclined guiding surfaces 38 that are located on the front side in the locking direction of both side surfaces in the circumferential direction of the drive-side convex sections 34 that are formed on the drive-side cam surface 31 slide along and are guided by driven-side inclined guiding surfaces 39 that are located on the rear side in the locking direction of both side surfaces in the circumferential direction of the driven-side convex sections 36 that are formed on the driven-side cam surface 32, and go up the driven-side inclined guiding surfaces 39. As a result, as illustrated in FIG. 12C, the flat tip-end surfaces 40 of the drive-side convex sections 34 and the flat tip-end surfaces 41 of the driven-side convex sections 36 come in contact with each others, the dimension in the axial direction of the cam device 25 expands and the locked state is set, and the space between the inside surface of the pair of support-plate sections 22 decreases. Consequently, the surface pressure at the areas of contact between the inside surfaces of the pair of support-plate sections 22 and the outside-surfaces of the pair of held plate sections 21 increases, the inner diameter of the front-end section of the outer column 18 elastically contracts, the surface pressure at the area of contact between the inner-circumferential surface of the front-end section of the outer column 18 and the outer-circumferential surface of the rear-end section of the inner column 19 increases, and the steering wheel 1 is held at the adjusted desired position.
In a steering wheel position adjustment device in which a cam device 25 such as described above is assembled, in the locked state the drive-side cam 27 and the driven-side cam 28 rotate relative to each comparatively easily, and there is a possibility that a problem will occur in that the locked state will easily become released when an impact is mistakenly applied to the adjustment lever 23.
JP2002087286 (A) describes construction in which by forming gradient sections on the tip-end surface of drive-side convex sections that are provided on a drive-side cam, such that the gradient sections are inclined in the opposite direction from drive-side inclined guiding surfaces that are formed on the side surfaces in the circumferential direction of the drive-side convex sections, it becomes difficult for the drive-side cam to rotate relative to the driven-side cam in the unlocking direction. However, in the case of the construction described in JP2002087286 (A), the gradient sections wear after use over a long period of time, and there is a possibility that the gradient sections will not be able to effectively prevent relative rotation between the drive-side cam and the driven-side cam, and there is a possibility that the operating force of the adjustment lever when the tip-end surfaces of the driven-side convex sections ride up on top of the gradient sections will become too large, and operability of the adjustment lever will decrease.